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29
FROM NZMJ
first author (with both authors having experience in studying such
signage).6 The same facilities were then examined using Google
Street View (GSV) by an independent observer not involved in the
field work (AT—see acknowledgements). This was after training
in using GSV with a sample of hospitals elsewhere in the country.
The second step was to study a random sample of 20 public
hospitals from around New Zealand (a 26% sample from the list
of 86 hospitals,8 and excluding the 10 hospitals sampled above,
and using the random number function in Excel). The selected
hospitals ranged from having 8 to 863 beds (median: 70) and
covered 12 DHBs. These hospital sites were then examined, using
GSV, for smokefree signage at the main driveway entrance (by
NW in April 2015). See Table 1 for additional definitions and other
details.
Results
In the field observations (Table 1), 90% of hospitals had
smokefree signs at the main entrance, and 90% had at least one
such visible sign anywhere else on the premises when walking
around the perimeter (on stand-alone sign posts, fences or
buildings). The average number of signs observed per hospital was
8.6 (range: 0–27; total: 86). But field observation found that only
40% of hospitals had any signs that stated that the ‘grounds’ were
smokefree.
The comparable figures from the independent observer using
GSV were: 90% at the main entrance, 90% for any other signs,
and the average number of signs was 3.5 (range: 0–21; total: 35).
Only 40% of hospitals studied with GSV had any observed signs
that stated that the ‘grounds’ were smokefree.
Assuming that all the field observations were ‘correct’, the
observations using GSV had very good sensitivity, specificity and other
characteristics (Table 1), albeit somewhat less favourable for signs
mentioning ‘grounds’.
The random sample of 20 hospitals nationally using GSV indicated
that only half (10/20) had any visible smokefree signage at the main
entrance (Table 2). Only around a third (35%; 7/20) had smokefree
signage that included words relating to the ‘grounds’ being smokefree.
Table 1: Sensitivity, specificity and predictive value of Google Street View (GSV) relative
to field observations of smokefree signage at a convenience sample of 10 New Zealand
hospitals
Performance characteristic
of GSV vs field observations
Any smoke-
free signs
at main
entrance*
Any other
smokefree
signs on
premises
At least one
smokefree
sign mentions
smokefree
‘grounds’
(or site or cam-
pus)
True positives (number) [A]
9
6
3
True negatives (number) [B]
1
4
5
False positives (number) [C]
0
0
1**
False negatives (number) [D]
0
0
1
Total (number)
10
10
10
Sensitivity [A/(A+D)]
100%
100%
75%
Specificity [B/(B+C)]
100%
100%
83%
Positive predictive value [A/
(A+C)]
100%
100%
75%
Negative predictive value [B/
(B+D)]
100%
100%
83%
* That is within 10 metres either side of the edges of the main entrance (defined as the main
driveway for all 10 hospitals in this sample) and including blurred signs based on these being likely
(50%+ probability) to be smokefree signs when considering colour and shape to the experienced
and trained observers. Blurring could be due either to distance or sometimes to the automatic
blurring function used by GSV for vehicle number plates.
** This result might not have been a problem with GSV based observations, but rather the field
observers may have missed a sign saying “grounds”.